Nitrogen oxides play an important role in smog formation and otherwise contribute to the pollution of the atmosphere. The removal of nitrogen oxides from exhaust gases of various kinds has been the goal of many different types of chemical processes which treat such gases. Power plant stack gases, for example, have been treated in various ways prior to venting to the atmosphere. With the recent government regulation of air quality, the need for removing pollutants such as NO.sub.x from gases released to the atmosphere has increased considerably.
Among the processes which have previously been used for NO.sub.x removal are thermal and catalytic reduction, especially selective catalytic reduction utilizing noble metal and base metal catalysts, absorption in scrubbing solutions, for example, EDTA and ferrous ion-containing solutions, and the use of molecular sieves.
One method which is used extensively is the selective reduction of NO.sub.x with ammonia (NH3) to form N.sub.2 and H.sub.2 O. Although effective, the possibility of chemical spills in the transportation of anhydrous ammonia has raised growing concern because of the volatility and corrosive nature of this toxic material. It would be desirable to minimize the risk of injury from NH.sub.3 spills while still retaining the capability of using the reducing power of ammonia in NO.sub.x abatement. Urea has also been used as a NO.sub.x reductant. However, urea, which is a solid presents handling problem as well.